In order to solve the calibration problem of radiation heat flux sensors in vacuum environments, a 50 mm large?diameter vacuum high?temperature blackbody radiation source device was developed by using pyrolytic graphite as the heating element, and measuring and controlling the temperature using a standard photoelectric pyrometer, and the performance indexes of the device were tested and evaluated. The temperature stability of the device within 10 min was not more than 0.5℃, and the radial temperature uniformity was not more than 0.1%t (t is the set temperature), which met the requirements of relevant regulations. Finally, the uncertainty components introduced by the performance indexes of the vacuum high?temperature blackbody radiation source in the process of heat flow calibration were calculated and analyzed. The research results provide strong support for promoting the application of the device in the calibrations of heat flow, radiation temperature and other fields.